An axle truss is a device that is attached to an axle to give it added support and strength against bending or deflecting out of alignment. Commonly manufactured from round steel bar stock or square tubing, the axle truss spans the width or the axle from wheel hub to wheel hub while coming in contact with the axle's center section. For vehicles that will experience heavy loading from either carrying a large load or from hitting the ground hard after jumping over an obstacle, as vehicles used in desert racing, the axle truss is typically mounted under the axle to offer support vertically. For high-performance vehicles that will experience severe gravity-force (G-force) as in drag racing's severe acceleration, the truss will commonly be welded to the rear of the axle housing.
Even though a rear axle is built from heavy materials, the axle tubes are welded into the center section, which creates a weak link on each side of the housing. Under severe use, the rear axle can bend or break, causing catastrophic failure of the axle and potentially wrecking the vehicle. By installing an axle truss, the force exerted upon the axle is spread out across the entire width of the axle, thereby creating a much more rigid structure. On four-wheel drive vehicles, such as those used in off road racing, this applies to both the front and rear axles.
Often, small stringers will be connected between the arch of the main axle truss and the axle tubes. This creates an axle truss system similar to what is used on suspension bridges, where the main cables are aided by small drop cables. Doing this will make the strength of the axle housing even greater. This method of creating strength is typically used when round bar or flat steel is used to manufacture the axle truss. When square tubing or three-sided tubing is used to support the axle, the axle truss is typically welded to the back of the axle housing, essentially tying the axle tubes to the center section. This is best accomplished with the axle housing mounted in a jig to prevent the heat from the welds from distorting the shape of the housing.
Using an axle truss on a drag racing vehicle is often the best method of avoiding a broken rear axle housing. The size of the tires combined with the extreme power of the engine and the traction created can often cause the tires to attempt to drive around the axle housing. This often leads to one or both axle tubes breaking off of the center section of the rear axle.